Morris Minor Owners Club

Rather disappointing ———-

The acton of citric acid can be very slow when cold. For an engine it really isn't practical to have a heated bath of it so I would suggest getting the engine running in the car and add citric acid to the coolant. Run up to temperature and repeat this several times then drain and flush.

I have de-rusted parts in a stainless steel preserving pan on the gas stove. It is very quick with the citric acid solution close to boiling. At garage temperature in autumn it takes weeks and even then I'll be agitating with a wire brush periodically as well.

Stephen

Thanks Stephen, the water solution was very hot when poured into the block, it’s been there for a total of 3 weeks, now looks like the surface of the iron has a film of some kind of crystalization, presumably from the acid. I’ve treated the head for 1 week and that looks fine.

I agree with Stephen. You need to do it in an installed engine, a strong solution and leave it in for a week with plenty of heat cycles. My friend did his 1966 Austin Healey this year. It looked much like yours before hand, but 3 applications, a week at a time, cleaned it completely.
Paul

les wrote: ↑Sat Oct 17, 2026 4:54 pm Thanks Stephen, the water solution was very hot when poured into the block, it’s been there for a total of 3 weeks, now looks like the surface of the iron has a film of some kind of crystalization, presumably from the acid. I’ve treated the head for 1 week and that looks fine.

The trouble is that your hot solution would have cooled extremely fast with the heat sink of a cast iron block. The crystals look like limescale but they might be citric acid crystals. It will all dissolve with a hot solution and the water pump circulating the solution.

Stephen

A Post script. He used 50g per litre of citric acid, the followed up with Sodium Bicarbonate to neutralise it, about 1.3 times as much per litre. The chemical reaction also created some agitation, which helped shift some residues…

Les
I used citric acid on two 948cc Minor engines. Both were left soaking for approx the same time. One block came up like yours and the other is perfect.
My thought is that there has been a reaction to what was in the block i.e. type of anti-freeze for example to create the crystallisation.
I would suggest that you try Sodium Bicarbonate to neutralise as suggested by MinorOCD.
Phil

Thanks to all, well I refilled today hoping for a better result, thinking about it, that’s probably wishful thinking, so in view of suggestions maybe I’ll drain and try Sodium Bicarbonate. How is it used in this situation ?

Sodium Bicarbonate is a weak alkali and will do precisely nothing for the engine deposits on its own. It can be used to neutralise the citric acid which will give a fizzing action.

Stephen

Those deposits look similar to the green crystals I found in my water pump. I ordered citric acid after failing to find it locally. Arrived yesterday. I plan to mix some and add it to the cooling system then start and run the engine up to temperature each day next week. Flush with water then neutralize and flush again??
Any chemists out there? Is sodium bicarbonate best or sodium carbonate, or sodium hydroxide, or something else better? Will neutralizing leave a reactive salt that will attack the coolant or system components?

There's really no need to neutralise with anything if the flushing is thorough. Citric acid is the acid that makes lemons sharp. It is widely used as a de-scaler for kettles, washing machines, dishwashers etc.

Stephen